The invention relates toga pressure medium activated piston-cylinder device including a cylinder with two end walls having pressure medium communication ports, a piston movably guided in the cylinder and connected to a piston rod which extends out of the cylinder through a sealed-off passageway in a first one of the end walls, a piston rod locking device located in the passageway and including at least one piston rod engaging clamping element which is axially locked relative to the first end wall, and an activating member continuously spring biassed toward a clamping element activating position and shiftable by pressure medium toward a release position against said spring bias as pressure medium is supplied to the cylinder via either one of the communication ports.
Piston-cylinder devices of this type are previously well known for various applications, See for instance U.S. Pat. No. 5,761,984, GB 997,815 and EP 103 555. They all suffer from a drawback relating to their pressure medium released piston rod locking mechanisms which lock automatically the piston rod and the object connected thereto in the very position occupied at the moment the medium pressure is interrupted. The drawback resides in the fact that there is no possibility to move manually the piston rod and the connected object without pressure medium being available. This may be particularly serious in some emergency cases where the connected object has to be moved immediately.
The primary object of the invention is to provide a piston-cylinder device of the above described type, wherein the piston rod locking device is releasable by means of a manually operable release mechanism.
Another object of the invention is to provide a piston-cylinder device of the above related type with a manually operable release mechanism which is simple and compact in design and which does not add considerably to the outer dimensions of the device.
A further object of the invention is to provide a piston-cylinder device of the above type wherein a manually operable release mechanism is designed so as to be easily operable by a low manual force.